Final answer:
The S phase lasts around 8 to 10 hours and during this time, DNA replication occurs. Around 50% of the DNA is thought to replicate at any given time in a typical eukaryote.
Step-by-step explanation:
The S phase, or synthesis phase, is a stage in the cell cycle where DNA replication occurs. It typically lasts between 8 to 10 hours. During this phase, the DNA in the nucleus is replicated and identical copies, called sister chromatids, are formed. These sister chromatids remain attached at the centromere.
In a typical eukaryote, only a fraction of the DNA replicates at any given time. The exact fraction can vary, but typically around 50% of the DNA is thought to replicate during the S phase. This ensures that each cell receives a complete set of genetic information during cell division.